DESCRIPTION: (Adapted from the abstract) A non-invasive, in vivo model for mechanically induced stimulation of the tibia of rats will be used to further define the response of cortical bone to mechanical loads. Specifically, the study will focus on the bone modeling response of the tibia to mechanical bending. It is anticipated that the modeling response will be either lamellar or woven bone formation on the periosteal and endosteal surfaces. This study has six major objectives 1) to determine the number of cycles per day of mechanical stimuli that cause lamellar bone formation and the number that cause woven bone formation, 2) to determine the mechanism of increase of lamellar bone formation in response to increasing mechanical stimulus, 3) to quantify the stress/strain signals in the bone and correlate their magnitudes to the bone formation response after 12 days, 4) to demonstrate the effects of blocking prostaglandin synthesis on adaptive bone modeling, 5) to find the time needed for rat bones to fully adapt to mechanical bending, and 6) to quantify the stress/strain signals in fully adapted bone and correlate their magnitudes with their initial magnitudes before adaption took place. This study uses the engineering methods of finite element analysis, beam bending analysis, and in vivo strain gage measurements to quantify the stress/strain signals created by bending the tibia. Histomorphometry of fluorochrome bone labels will be used to quantify the new bone formation.